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The present invention relates to trunking techniques employed in data communication systems and more specifically to a method and apparatus for directing a packet received at a first Mux/Demux device at a communications link comprising a link within a first trunk group to a another link coupled to an output of a second Mux/Demux device and comprising a link within a second trunk group.
As is known in the art, data contained on a higher speed local area network link may be communicated over a plurality of lower speed network links that are organized as a trunk group. In this manner the lower speed links that typically employ older technologies may be aggregated to carry higher bandwidth data. Trunk Mux/Demux devices are commonly used for multiplexing packets received over multiple input links of a trunk group to a single output link or demultiplexing packets received over a single high-speed link for transmission over selected lower speed links of a trunk group.
There are well known limitations with respect to trunking systems which result in a statistical bandwidth and an average bandwidth performance that is less than the sum of the lower speed trunk group links. Whole packets are sent down individual links and streams of packets having the same source and destination addresses are sent down the same link to maintain packet order. Packet ordering is typically required for correct operation by a number of higher level protocols. A need to maintain complete packets and to keep packets in order places higher bandwidth demands on the traffic carrying links and may preclude the trunk from obtaining the theoretically achievable bandwidth.
In typical trunking systems, mapping is accomplished via use of a hashing algorithm on source and destination addresses (either layer 2, layer 3 or both) or priority (based upon explicit tags, such as the Internet Protocol (IP) Type of Service (TOS) tag, differentiated services or 802.3 QoS fields. These methods result in a dynamic or statistical mapping of packets received via a first trunk group coupled to source ports in a first Mux/Demux to destination ports in a second Mux/Demux. As such, no minimum packet loss or bandwidth utilization of destination ports of the second Mux/Demux which are coupled to respective links of a second trunk group can be guaranteed.
It would therefore be desirable to have a system for efficiently mapping packets received over n communication links of a first trunk group at n corresponding ports of a first Mux/Demux device for transmission over m communication links of a second trunk group driven by m corresponding ports of a second Mux/Demux device that is communicably coupled to said first Mux/Demux device via a high-speed communications link.
A method and apparatus for coupling a first trunk group comprising n links to a second trunk group comprising m links is disclosed. A first Mux/Demux device receives packets over the n communication links at n corresponding ports of the first Mux/Demux device. The n communication links comprise links of the first trunk group. The first Mux/Demux device inserts within the received packets a port identifier tag that identifies the port at which the respective packet has been received. The packets are transmitted by the first Mux/Demux device over a high-speed link for receipt by a second Mux/Demux device. The second Mux/Demux device has m output ports for communicating over m corresponding links of the second trunk group. A port translation table is maintained at the second Mux/Demux device. The port translation table is indexed by the port identifier tag within each received packet to obtain the identity of the specific output port of the second Mux/Demux device to be employed for the transmission of the respective packet. The packets are then transmitted out of the port specified by the port translation table. Auto-configuration of the port translation table may be employed in accordance with predetermined mapping techniques to identify the links of the second trunk group to be employed for packets received over links of the first trunk group.
Other features, functions and aspects of the invention will be apparent from the Detailed Description of the invention that follows.